As we were all scratching our heads.. apparently knocked discharge temp down enough to throw the rest out of line.? Thermistor was checked as was line temp, flow was verified with buckets etc. System was my own so many evenings after work info was gathered/checked. wf was going to fly a tech out until he said he had seen the issue before.. I changed to a closed loop and it's been trouble free ever since. Have not seen the problem on any installs after that either, though I don't know of any with all the same scenarios needed to make it happen until reading this. Not sure if it's the same problem with the wtw unit but it sure sounds similar.